US20080005030A1 - Secure Escrow and Recovery of Media Device Content Keys - Google Patents

Abstract

An embodiment of a method for secure escrow and recovery of media device content keys includes generating, with a first processor of a media device, an escrow key for encrypting a plurality of content keys, the content keys for encrypting instances of media content. The first processor of the media device encrypts the escrow key with a public key of a key clearinghouse. The escrow key, encrypted with the public key of the key clearinghouse, is stored in a storage location outside of the first processor of the media device.

Description

BACKGROUND
• 1. Technical Field
• The present disclosure generally relates to securing data, and more particularly, to securing data associated with a digital media device.
• 2. Description of the Related Art
• A storage device, such as a hard drive of a digital media recording device, can be used to store media data associated with received audio and/or video content. For example, one such digital media recording device is a digital video recorder (DVR). A DVR application executed by the DVR provides user interface screens that can be used to manage the media data stored to the storage device. The DVR application can also be used to playback recorded media at a later time, while also having the ability to pause, rewind, and fast-forward through the recorded media.
• The media data stored to the DVR can be encrypted in order to protect the media content from unauthorized playback. A processor, which could be a secure microprocessor, associated with the DVR can be used to protect the encryption keys that are used by transport stream encryption processors to encrypt the content. In a typical embodiment, the content is encrypted with a content key, and then the content key itself is then encrypted with the public key of the secure microprocessor. Because the content key is encrypted, it can then be stored outside of the secure microprocessor, such as on a hard drive along with the associated encrypted media content.
• Upon request for playback of the media content, the associated encrypted content instance key is retrieved from the storage device and decrypted using the private key of the secure microprocessor. The media content can then be retrieved and the decrypted content key can then be used to decrypt the media data for playback.
• However, because the encrypted content key is associated with the private key of a particular secure microprocessor, when a DVR and/or its secure microprocessor fails it is not be possible to access the secure microprocessor to allow decryption of the content key, and to decrypt stored content from the DVR's storage device. Thus, the DVR owner's library of recorded and encrypted media content becomes inaccessible for playback. This may be so, even though the user may be legally entitled to play the media content, e.g., after paying for that right. Additionally, tying the media content to a particular DVR introduces problems with respect to the sharing of digital media between devices. For example, in some cases, a subscriber may be authorized to view content recorded by a first DVR within the subscriber household on another, second media device (i.e. a set-top box or another DVR, among other possible media devices) within the subscriber household. However, because the encrypted media content is tied to the secure microprocessor in the first DVR used to record the media, such sharing becomes difficult.
• To allow for recovery of a content key in the event that the original secure microprocessor is destroyed or missing, the content key can be encrypted with the public key of a cable head-end system. Accordingly, a DVR having a new secure microprocessor sends the encrypted content keys on a program-by-program basis to the head-end for decryption and the head-end recovers content keys by decryption with its private key. The content keys can be re-encrypted with the public key of the new secure microprocessor and sent back to the DVR.
• However, there are a number of drawbacks to such a recovery scheme. For example, public key encryption and decryption are computationally expensive operations, requiring hundreds of milliseconds (or even seconds) of processor time. Because the public key encryption and decryption of content keys are performed within the secure microprocessor as an atomic operation, they can interfere with other timing-sensitive operations that the secure microprocessor is responsible for, such as conditional access (CA) decryption. This is particularly true if the secure microprocessor is decrypting electronic control messages (ECMs) for multiple streams from the multiple system operator (MSO) network. Additionally, a second problem is that recovery of the original secure microprocessor requires the cable head-end to recover content keys for each and every program on the DVR hard drive. This approach does not scale well in a system with thousands of DVR set tops, each with potentially hundreds of programs to be recovered.
• Therefore, what are needed are systems and methods that can potentially address one or more of the aforementioned deficiencies.
BRIEF DESCRIPTION OF THE DRAWINGS
• The components in the drawings are not necessarily to scale relative to each other.
• Like reference numerals designate corresponding parts throughout the several views.
• FIG. 1 depicts a simplified block diagram of an embodiment of a secure escrow and recovery system that can be used for managing encryption keys used for securing and accessing media content associated with one or more digital media devices.
• FIG. 2 depicts a block diagram of an exemplary arrangement of a secure escrow and recovery system depicted in the diagram ofFIG. 1.
• FIG. 3 depicts a block diagram of selected system components of a key clearinghouse of the secure escrow and recovery system ofFIG. 1.
• FIG. 4 depicts a block diagram of selected system components of an exemplary embodiment of a remote device such as the digital-video recorder (DVR) ofFIG. 2.
• FIG. 5 depicts a data flow diagram illustrating an embodiment of a system and/or method for initializing a secure microprocessor with an escrow key.
• FIG. 6 depicts a data flow diagram representing an embodiment for using the escrow key ofFIG. 5 for securing media content encrypted by the DVR ofFIG. 4.
• FIG. 7 depicts a data flow diagram representing an embodiment for using the escrow key ofFIG. 5 for playback of encrypted media content on the DVR ofFIG. 4.
• FIG. 8 depicts a data flow diagram representing an embodiment of a content recovery process that could be used to allow a replacement secure microprocessor to access media content encrypted previously by the original secure microprocessor.
• FIG. 9 depicts a data flow diagram representing an embodiment for replacing escrow key security packages created by an original secure microprocessor with corresponding escrow key security packages created by a replacement secure microprocessor.
• FIG. 10 depicts a data flow diagram representing an embodiment for using an escrow key to facilitate the ability for multiple remote media devices, such as the DVRs ofFIG. 2, to share media content.
DETAILED DESCRIPTION
• The present disclosure relates to a media content encryption scheme that makes use of a two-level symmetric key encryption scheme for media device recording and/or playback. Systems and methods are described for set-up/initialization of a digital media device, subsequent recording and playback on a digital media device, and key recovery. Additionally, embodiments for media sharing between two media devices using the disclosed encryption schemes are also disclosed.
• According to embodiments of the present disclosure, reference is made to an escrow key, which may also be designated in the figures and description as “K_ESCROW.” The term escrow is generally known to refer to the concept of a third party holding an object (i.e. money, an instrument, merchandise, assets, etc.) on behalf of at least two other parties in a transaction. A first party gives the object to the third-party escrow, who holds it for a second party until appropriate instructions are given to the third-party escrow or until the third-party escrow knows that the second party has fulfilled particular obligations.
• Similarly, in the disclosed embodiments, the escrow key K_ESCROcan be viewed as the object in an escrow transaction.FIG. 1 depicts a simplified block diagram of an embodiment of a secure escrow andrecovery system100 that can be used for managing encryption keys used for securing and accessing media content associated with one or more digital media devices, such as a DVR set top, among other devices capable of recording and/or playback of digital media.
• The keys can be managed, in part, using secure microprocessors. Secure microprocessors, or other secure encryption devices, may be configured as a physically secure environment such that, subsequent to manufacture, operations within the secure microprocessor are unobservable. More specifically, in at least one embodiment, the secure microprocessor can be viewed as a secure environment, where calculations and other operations performed within the secure environment are not viewable by other components outside of the secure microprocessor.
• A first secure microprocessor102 (i.e. of a media device, such as a DVR) generates anescrow key104, which is used for encrypting content keys that are used for encrypting instances of media content. The escrow key is ultimately to be provided to a secondsecure microprocessor106. However, a third party escrow, here referred to askey clearinghouse108, can be used to perform the function of preventing the secondsecure microprocessor106 from accessing theescrow key104, (i.e. physically, using encryption, etc.) until certain obligations are met. In some embodiments,key clearinghouse108 could be, for example, a cable head-end or other remote server that is communicatively coupled to the first and second microprocessors.
• An exemplary obligation thatkey clearinghouse108 enforces is a verification that the secondsecure microprocessor106 has the necessary permissions to access the escrow key K_ESCRO. Such permissions may be dictated by digital rights management (DRM) criteria and/or other media content authorization logic. According to some embodiments, the secondsecure microprocessor106 sendsverification information110 to thekey clearinghouse108, which could include identification information of the firstsecure microprocessor102, among others.Key clearinghouse108 then verifies that the secondsecure microprocessor106 and/or its associated media device has the appropriate permissions (i.e. satisfied the proper obligations) to access the escrowkey K_ESCRO104. Accordingly, if the secondsecure microprocessor106 is deemed to have the necessary permissions, K_ESCRO104 is transmitted to the secondsecure microprocessor106 to allow it to decrypt content keys which can be used to decrypt media content encrypted by the firstsecure microprocessor102.
• In some instances, although the firstsecure microprocessor102 generates the escrowkey K_ESCRO104, it is not necessary that the firstsecure microprocessor102 or its associated media device transmit the escrowkey K_ESCRO104 tokey clearinghouse108. Rather,K_ESCRO104 can be encrypted by the firstsecure microprocessor102 such that the secondsecure microprocessor106 can not directly access theK_ESCRO104. Thus, the secondsecure microprocessor106 could be allowed access to the encrypted escrowkey K_ESCROW104 without satisfying any particular obligations. For example, among other possibilities, a storage device holding theencrypted K_ESCRO104 could be made accessible to the second secure microprocessor. However in order to access the escrowkey K_ESCRO104 in the clear,key clearinghouse108 is used for decrypting the escrowkey K_ESCROW104 and providing it to the secondsecure microprocessor106.
• Once obtained in the clear, the escrowkey K_ESCRO104 can be used by the secondsecure microprocessor106 to decrypt the content keys that were used to encrypt the instances of media content. The recovered content keys can then be used for decrypting the associated instance of media content.
• Systems and methods that describe such an operation in more detail, among other embodiments, are described herein. It should be understood that, omitted from the figures are, in accordance with some embodiments, a number of conventional components known to those skilled in the art that are unnecessary to explain the operation of the disclosed systems and methods for secure escrow and recovery of media device content keys.
• FIG. 2 depicts a secure escrow andrecovery system100 in which embodiments of the described secure escrow and recovery of media device content keys may be implemented.System100 may be used, among other purposes, for coordinating the exchange of information capable of being used to secure media content stored on devices located remote from a media content source, such as, among others, a cable-television or digital satellite television provider, for example.
• Media content could comprise audio, video, images, text, teletext, among others. According to some embodiments, media content, as referred to herein, may also be referred to as media programs or media programming. Some examples of media programming used herein include, but are not be intended to be limited to, television programs and radio programs. Such television programs and/or radio programs could be scheduled broadcasts or delivered to a user on-demand (e.g. such as provided with a video-on demand system). The media content could be unicast to a single user, or could be multi-cast or otherwise broadcast to multiple users.
• An instance of media content (or media programming, etc.) could be, for example, a television show (e.g. an episode of Smallville) or other segment of recorded media content. A series of media programming could be, for example, a number of episodes of a television show (e.g. the last five recordings of Smallville). The media content can be received and recorded by the remote devices. For example, the media content can be stored to a storage medium as media data. In some instances, such media data is encoded audio and/or video signals, among other potential representations of the media content that is in a form suitable for processing by media devices.
• According to some embodiments,media content source202 delivers media content to a number of remote devices over atransmission medium206, which may be one or more of, among others, twisted-pair telephone wire, coaxial cable, optical fiber, over-the-air waves, etc. The remote devices may be located at, for example,user premises104.
• Accordingly, the media content may be received by a remote device within theuser premises204 that is capable of receiving and, possibly, decoding the media content. The remote device may, for example, form part of, be associated with, or be integrated in one or more of a cable-television set-top box, a television, portable device, digital video recorder (DVR), personal video recorder (PVR), a personal digital recorder (PDR), and/or a personal computer, laptop computer, or personal digital assistant (PDA), among others.
• For the purposes of illustration, one such remote device configured to execute media recording capabilities isDVR208.DVR208 may be configured to record received media content and store associated media data on a storage medium. According to some embodiments, the media data may be later accessed for playback on a playback device, such astelevision210, at a later time. The playback device could also be one or more of a computer monitor, an audio receiver, or other device capable of emitting sound or images pertaining to the media content.
• According to some embodiments, in addition toDVR208, auser premises204 can have other media devices (i.e. other DVR'S, cable set-top boxes or other digital media receivers, etc.). According to some embodiments, these other media receivers can be in communication withDVR208. Depicted in the upper right portion ofFIG. 2, for example, asecond DVR208ais associated with the respective user premises.DVR208a, according to some embodiments, is associated with arespective display device210a. In some instances,DVR208ais in communication withDVR208 overcommunication medium212. For example, thecommunication medium212 could be twisted pair, Ethernet, or any type of wired or wireless network.DVR208 andDVR208a, and any other DVRs that may be present atuser premises204, may communicate directly or through one or more other devices in a local-area-network (LAN). In some cases,DVRs208 and208acan share media content and/or programming guide information, among other DVR related information, over thecommunication medium212.
• Although embodiments are described within the environment of a cable-television system, it should be understood that other media delivery and/or receiving devices are intended to fall within the scope of the invention. For example, themedia content source202 could be a satellite television provider or even a media server on the Internet. The remote device could be a satellite television decoder, a computer configured to receive the media content, or could be any device, such as a personal computer, that is configured with media recording and/or playback ability. Additionally, although the media content may be described as comprising video and audio content, some embodiments may include only audio or only video. The media content could even comprise text or other forms of media. Further, in some instances, non-media information (e.g. security keys, digital-rights management (DRM) information, etc.) may be transmitted along with the media content.
• According to some embodiments, as briefly described above,key clearinghouse108 prevents or provides access to an escrow key that has been used to encrypt other keys (i.e. content keys) used to encrypt instances of media content. Thus, in some embodiments,key clearinghouse108 facilitates secure escrow and/or recovery of media device content keys. Although in some embodimentskey clearinghouse108 stores the escrow keys in order to facilitate later recovery, in some embodimentskey clearinghouse108 does not store the escrow key at all before recovery is requested. Rather, in the latter case,key clearinghouse108 is configured to recover content keys when provided with the encrypted escrow key.
• Key clearinghouse108 and/ormedia content source202 may form or be associated with, among others, a cable head-end system or other remote media delivery system. However, in some embodiments,key clearinghouse108 is any device communicatively coupled to therespective DVRs208. For example,DVRs208 can communicate withkey clearinghouse108 over a network, such as a LAN, WAN, and/or the Internet. It is not necessary thatkey clearinghouse108 be associated with themedia content source202.
• FIG. 3 depicts a simplified block diagram of thekey clearinghouse108 of the secure escrow andrecovery system200 ofFIG. 2. Associated with thekey clearinghouse108 is a secure encryption device302 and a clearinghousekey storage314. Secure encryption device302 includesmemory310 for holding a plurality of keys used for encrypting and decrypting data. For example,memory310 may store a privatekey K_CH-PRIVATE312 of thekey clearinghouse108.
• Secure encryption device302 may further include an encryption/decryption processor308 for retrieving keys and using them to encrypt and decrypt data transmitted between one ormore DVRs208. According to some embodiments, clearinghousekey storage314 is used to store, among others, one ormore escrow keys104 that are associated with the one ormore DVRs208. In some embodiments, escrow keys are stored securely (i.e. encrypted) in an escrowkey package316. Clearinghousekey storage314 can also store public keys318 (designated as “K_SM-PUBLIC) associated with each secure microprocessor ofDVRs208.
• FIG. 4 is a block diagram depicting selected system components of an exemplary embodiment of theDVR208 ofFIG. 2.FIG. 4 depicts several components commonly communicating through alocal bus400. For example,DVR208 may include acommunications interface402 for receiving video, audio and other media signals from a media signal source, such as the media content source202 (FIGS. 1 and 2). Thecommunication interface402 may include a tuner system (not depicted) which could include, for example, a tuner for receiving and selecting one or more selected channels or digital streams of media signals. Such a tuner system can tune to a particular television station or digital stream, and the media signals associated with this station or stream can be recorded by theDVR208.
• DVR208 can further include at least oneprocessor406 for controlling the operations of theDVR208 and anoutput system408 for driving a playback device (e.g., television210). Aninput system410 can receive user inputs provided via a wired or wireless input device such as, for example, a hand-held remote control, a transmitter with buttons or keys located on the exterior of the DVR, and/or a keyboard.
• According to some embodiments,communication interface402 transmits and/or receives data over a network such as a LAN, WAN, or the Internet. For example, data may be transferred to/from another DVR, received from media content source202 (FIG. 2), or from a centralized server through communication interface412. Such data could be media signals and or other data, such as programming information, or other data capable of being stored and or displayed to the user.Network interface312 may comprise, for example, an Ethernet interface, an IEEE-1394 interface, a USB (Universal Serial Bus) interface, a serial interface, a parallel interface, a wireless radio frequency (RF) interface, a telephone line interface, a power line interface, a coaxial cable interface, and/or an infrared (IR) interface, among others.
• Memory414, which may include volatile and/or non-volatile memory, can store one or more programmed software applications, herein referred to as applications, which contain instructions that may be executed byprocessor406 under the direction ofoperating system424. Input data used by an application can be stored in memory414 and read byprocessor406 as needed during the course of the application's execution. This input data may be data stored in memory414 by a secondary application or other source, either internal or external toDVR208, or may be data that was created with the application at the time it was generated as a software application program.
• Internal storage418 may comprise a recordable medium and may be a number of devices available for non-volatile data storage, such as a hard disk drive (HDD), optical drive, or flash memory, for example.Internal storage418 may be used for storing data, including media data and non-media data. Media data could represent media content received throughcommunication interface402. According to some embodiments, it should be understood that media programming can be digitally encoded before being stored on recordable medium by the DVR itself or by means external from the DVR, such as the media signal source or a cable set-top box.
In some embodiments,internal storage418 is also used for storing non-media data, such as encryption keys, DRM information, and programming guide information associated with stored media data.
• Likeinternal storage418,external storage420 also comprises a recordable medium and may be a number of devices available for non-volatile data storage, such as an HDD, optical drive, or flash memory, for example. However, unlikeinternal storage418, which is located within the DVR enclosure (i.e. housing)419,external storage420 can be removably attached toDVR208 through acommunications interface422, which could be any number of wireless or wired interfaces, for example.
• Although only one external storage device may be used in some embodiments, it is contemplated thatexternal storage420 may comprise a plurality ofstorage devices420a-420n. For example,devices420a-420ncould be a plurality of HDDs. It can be appreciated that the one or more HDDs could be daisy chained, or otherwise linked, to communicate withDVR208 over thecommunications interface422.
• Although memory414,internal storage418, and/orexternal storage420 have been described as potentially performing particular functions, according to some embodiments, these particular functions could be shared, or carried out completely, by any other of the memory and/or storage devices.
• Communication interface422 could be a bus operating under the Advanced Technology Attachment (ATA) standard, and more specifically, the Serial-ATA (i.e. SATA) standard version 2.5, which is available from the Serial ATA International Organization and is hereby incorporated by reference in its entirety. According to such an embodiment,DVR208 may include a communications interface comprising an attachment port on thehousing419 of the DVR that cooperatively mates with the plug ofexternal storage420. A cable complying with the high-speed bus (i.e. a cable complying with the SATA standards) may provide the transmission medium betweenexternal storage420 and theDVR208. According to other embodiments,communications interface422 could be a bus complying with the IEEE 1394 (Firewire), the Universal Serial Bus (USB), or IEEE 802.11 standards. It can be appreciated that a number ofother communication interfaces422 could be used.
• One, or both of,internal storage418 and/orexternal storage420 could be used for recording media content to a transportable medium that is capable of being easily moved between a plurality of remote devices. For example,internal storage418 and/orexternal storage420 may be an optical drive configured to read and/or record to/from an optical medium. The transportable medium could also be flash memory such as used in USB thumb drives, smart digital (SD) memory or compact flash (CF) memory, among others. Accordingly,DVR208 may be configured to record media data, which could comprise moving or copying media data from other storage devices, to the transportable medium.DVR208 may also be configured to read media data from a transportable medium. Accordingly, the media data may be stored to a transportable medium, and the media data on the transportable medium may then be read by other devices, such as another DVR associated with a customer account. In that the media data is encrypted, embodiments disclosed herein describe systems and methods for sharing the media content between remote devices while maintaining the ability to decrypt the underlying media data by authorized devices.
• User input received during the course of execution of any processes implemented byDVR208 may be received from an input device (not shown) viainput system410, transmitted through thebus400, temporarily stored within memory414, and communicated toprocessor406. Data generated by an application can be stored in memory414 byprocessor406 during the course of the application's execution. Availability, location, and amount of data generated by one application for consumption by another application can be communicated by messages through the services ofoperating system424.
• Under user instruction,DVR application428 can perform the general tasks of recording and/or playback of received programs, among other tasks.DVR application428 can also provide a navigation framework for services provided byDVR208. Forexample DVR application428 can register for, and in some case reserve, certain user inputs related to navigational keys such as channel increment/decrement, last channel, favorite channel, etc.DVR application428 also provides users with television (or other programming) related menu options that correspond to DVR functions such as, for example, providing an interactive program guide, blocking a channel or a group of channels from being displayed in a channel menu, recording particular channels, playback of recorded shows, etc.
• Portions ofDVR application428 and/oroperating system424 may also facilitate the encoding/decoding and/or encrypting/decrypting of media data and/or other information used in the described systems and methods for securing media content using an interchangeable encryption key. Specifically,operating system424 orDVR application428 may use a secure element, depicted assecure microprocessor430, and/or DVR content decrypt/encrypt element442 to perform such encryption and/or decryption.
• For example, DVR content decrypt/encrypt element442 includes a processor for performing encryption and/or decryption of media content. For example, decrypt/encryptelement442 can decrypt the media content received from the media content source202 (FIG. 2) or from other DVR components, such asinternal storage418 orexternal storage420. DVR content decrypt/encrypt element442 also encrypts and/or re-encrypts media content for storage to the internal or external storage mediums.
• According to some embodiments, DVR content decrypt/encrypt element442 can obtain keys for performing such encryption and decryption of media content fromsecure microprocessor430.Secure microprocessor430 may include a processor, such as encryptor/decryptor432, for encrypting and decrypting keys used by DVR content decrypt/encrypt element442 to perform encryption and decryption of media content.
• In some embodiments,secure microprocessor430 includes amemory434 for storing a number of keys for encryption and/or decryption functions. For example,memory434 can include a privatekey K_SM-PRIVATE436 stored therein, and one or more escrow key storage locations for the storage of a respective escrowkey K_ESCRO104 and a storage location for storing the public key of thekey clearinghouse108, designated as K_CH-PUBLICkey438.
• Privatekey K_SM-PRIVATE436 can be used to decrypt data encrypted with a public key K_SM-PUBLIC(not depicted) associated with the privatekey K_SM-PRIVATE436. According to such embodiments,private key436 is typically kept from being exposed outside of thesecure microprocessor430 in clear form. The public key of the key clearinghouse K_CH-PUBLICkey438 could be pre-programmed, but is typically downloaded from thekey clearinghouse108 or other source. The public key of the key clearinghouse K_CH-PUBLICkey438 can be used to decrypt and/or verify that transmissions received fromkey clearinghouse108 are from a trusted source. The one or more escrow key storage locations for the storage of a respective escrowkey K_ESCRO104 can store keys generated by thesecure microprocessor430, and/or those generated by another secure microprocessor. Accordingly, in some embodiments,secure microprocessor430 also includes akey generator446 for generating keys, such as an escrow key.
• The applications executed byDVR208 can comprise executable instructions for implementing logical functions. The applications can be embodied in any computer-readable medium for use by or in connection with an instruction execution system. The instruction execution system may be, for example, a computer-based system, a processor-containing system, or any other system capable of executing instructions. In the context of this document, a “computer-readable medium” can be any means that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device.
• The computer-readable medium can be, for example, but is not limited to, an electronic, solid-state, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or propagation medium, either internal toDVR208 or externally connected to theDVR208 via one or more communication ports or network interfaces. More specific examples (a non-exhaustive list) of the computer-readable medium would include the following: an electrical connection (electronic) having one or more wires, a portable computer diskette (magnetic), a hard drive storage device (magnetic), a random access memory (RAM) (solid-state device), a read-only memory (ROM) (solid-state device), an erasable programmable read-only memory (EPROM or Flash memory) (multiple devices), an optical fiber (optical), and a portable compact disc read-only memory (CDROM) (optical). Note that the computer-readable medium could even be paper or another suitable medium upon which the program is printed, as the program can be electronically captured, via for instance optical scanning of the paper or other medium, then compiled, interpreted or otherwise processed in a suitable manner if necessary, and then stored in a computer memory.
• Now that a general overview of the various components of a system for secure escrow and recovery of media device content keys has been described,FIG. 5 depicts a data flow diagram illustrating an embodiment of a system and/or method for initializing a secure microprocessor with an escrow key.
• At block502 asecure microprocessor430 ofDVR208 generates an escrow key K_ESCROW. Atblock504 thesecure microprocessor430 stores the escrow key K_ESCROinto an escrow key storage location of memory434 (FIG. 4). The escrow key, in some embodiments, is a strong symmetric key. For example, among others, triple data encryption standard (3-DES) and advanced encryption standard (AES) are strong symmetric ciphers, given keys of sufficient length.
• According to some embodiments, thesecure microprocessor430 does not release the escrow key K_ESCROin decrypted form. Instead, atblock506, the escrow key K_ESCROWis encrypted with the publickey K_CH-PUBLIC316 ofkey clearinghouse108 to produce E(K_CH-PUBLIC(K_ESCROW)). In some embodiments,DVR208 may request the key clearinghouse public key and the key may be transmitted in response to such a request. However, in some embodiments,DVR208 has been provided with the public key ofkey clearinghouse108 previously.
• Once the escrow key K_ESCROis encrypted with the publickey K_CH-PUBLIC438 ofkey clearinghouse108, an escrow key package is created atblock508, which contains the encrypted escrow key. Specifically, in some embodiments, atblock508 thesecure microprocessor430 appends the current time and its identity to the encrypted escrow key E(K_CH-PUBLIC(K_ESCROW)) and then signs the entire message with its private key (i.e.,K_SM-PRIVATE436;FIG. 4) to produce the escrow key package. Accordingly, the signed encrypted message, which is referred to as an escrow key package, is then stored outside of thesecure microprocessor430. For example, the escrow key package can be stored tointernal storage418, or other devices associated withDVR208, and/or outside ofDVR208, such as within clearinghousekey storage314. According to such an embodiment,DVR208 can transmit the escrow key package over communications medium206 tokey clearinghouse108.
• Accordingly, once the initialization process has completed, an escrow key has been created and stored withinsecure microprocessor430. Additionally, in some embodiments, the escrow key has been encrypted with an asymmetric key, such as the public key ofkey clearinghouse108. The encrypted escrow key is then securely stored along with an identification of the secure microprocessor from which it was created and a time stamp. Because the escrow key (i.e. escrow key package316) is stored outside of the secure microprocessor in an encrypted state, onlykey clearinghouse108, or another entity having the private key capable of decrypting the escrowkey package316, is able to easily access the escrow key stored therein.
• FIG. 6 depicts a data flow diagram representing anembodiment600 for using the escrow key for securing media content encrypted by theDVR208. Upon starting a recording, thesecure microprocessor430 creates anescrow security package608 for the instance of media content. Theescrow security package608 can include, among other information, DRM information, the identity of thesecure microprocessor430 used to generate the escrow security package, the encrypted content key and the secure microprocessor signature to prevent tampering with the escrow security package.
• More specifically, atblock602, a content key used for encrypting an associated instance of media data, designated as K_C, is generated. Atblock604 the content key is encrypted with the escrow key K_ESCROpreviously stored within thememory434 ofsecure microprocessor430 to produce E(K_ESCROW(K_C)). Then, atblock606, theescrow security package608 is created which, in some embodiments, includes the DRM rights, identity of the secure microprocessor, the encrypted content key and/or the secure microprocessor signature. The escrow security package can be signed using the secure microprocessor private key, to prevent tampering. Theescrow security package608 is then stored outside of the secure microprocessor, such as tointernal storage418.
• At a time after content key K_cis generated atblock602, the content key K_ccan be provided to DVR content encryption/decryption element442 which is used to encrypt the instance of media content. Specifically, at block610,clear media data612, representing the instance of media content, is encrypted with the content key K_Cand theencrypted media content614, here designated as E(K_C(MEDIA DATA)), is then stored outside of the DVR content encryption/decryption element442. For example, theencrypted media content614 can be stored tointernal storage418.
• FIG. 7 depicts a data flow diagram representing anembodiment700 for using the escrow key for playback of encrypted media content. Although the present embodiment is described in terms of an embodiment for playback of media content, such an embodiment could also be used in other situations where access to clear media data is needed. Atblock702, the escrow security package that contains the content key associated with the desired media content to be played is delivered to thesecure microprocessor430 ofDVR208. At this time, theescrow security package608 can be checked for tampering (e.g. by verifying the signature on the escrow security package608). Atblock704, once theescrow security package608 has been checked,secure microprocessor430 decrypts the content key with the escrow key atblock704. The content key K_Cassociated with the desired media data can then be delivered to DVR content encrypt/decrypt element442, preferably through a secure connection.
• At block706, after receiving the encrypted media data E(K_C(MEDIA DATA)) frominternal storage418, the media data is decrypted. Specifically, because the media data is stored as encrypted with the content key, the content key delivered bysecure microprocessor430 can be used to decrypt the encrypted media data into clear media data708, which represents the desired media content. The clear media data708 could be used for a number of different purposes. However, in this case, theclear media806 data is provided fromDVR208 totelevision210.
• Accordingly, embodiments for initializing a DVR having an escrow key, using a DVR for the encryption of media data using the escrow key, and using the DVR for decrypting previously recorded content with the escrow key have been described. However, at some point the originalsecure microprocessor430 may not be available for decrypting media data stored to an associated storage device. For example, if thesecure microprocessor430 malfunctions, a new secure microprocessor may be installed within theDVR208. According to another instance, encrypted media data encrypted by a first secure microprocessor may be accessed by a second secure microprocessor, which may be in another DVR, for example. However, in both of these cases, the original secure microprocessor is no longer available to decrypt the escrow security package that is associated with the media data. Accordingly, because a different secure microprocessor does not have access to the original escrow key used to encrypt the content key K_Clocated in the escrow security package, the associated encrypted media data representing desired media content is no longer accessible. A number of other scenarios in which this might occur include an MSO upgrading the conditional access system (CAS) or a replacement of the entire set top (where the subscriber keeps the content).
• Notably, the escrow key package316 (FIG. 5) is not required for use in recording and/or playback. Rather, the escrowkey package316 is used during a key recovery process, which is described below.
• Accordingly,FIG. 8 depicts a data flow diagram representing anembodiment800 of a content recovery process that could be used to allow a replacement secure microprocessor to access media content encrypted previously by thesecure microprocessor430. In the instant case, it is assumed that theDVR208 is the same DVR used to record the media content as described with respect toembodiment600 ofFIG. 6. However,DVR208 now includes a second, replacementsecure microprocessor802 which replaces the originalsecure microprocessor430. However, it should be understood that theentire DVR208 could have been replaced, assuming the original encrypted media data and escrow security packages are retained. For example, the escrow security package and encrypted media data may be stored on anexternal drive420 and attached to the new DVR or a user or technician could installinternal storage418 within the new DVR. According to yet another embodiment, the encrypted media data representing an instance of desired media content and an associated escrow security package could be recorded to readily removable media, such as a CD ROM or DVD ROM, and made available to theDVR208.
• Atblock804 an escrow key recovery request is built. Specifically, according to one embodiment, an escrow key recovery request includes the escrowkey package316. However, if the escrow key package is already stored atkey clearinghouse108 it is not necessary to send the escrowkey package316 to the key clearinghouse. The escrow key recovery request can also include the identification of the replacementsecure microprocessor802, which could be a serial number or other unique identifier.
• According to embodiments in which the escrow security package is stored at the key clearinghouse, the escrow security package can include information used to identify the escrow security package that contains the needed escrow key. For example, identity information can be provided with the escrow key recovery request that matches information associated with an escrow key recovery package stored at the key clearinghouse. According to some embodiments, the identify information could comprise one or more of an identification of the secure microprocessor associated with the desired escrow key, timestamps, and/or serial numbers, among other identifying information.
• The escrow key recovery request is then transmitted tokey clearinghouse108 where, atblock806 the key clearinghouse authenticates the sender of the escrow key recovery request to confirm the identity of the replacementsecure microprocessor802. Atblock808, the key clearinghouse checks the signature on the escrowkey package316 to confirm the identity of the original secure microprocessor. Atblock810, thekey clearinghouse108 determines whether the replacementsecure microprocessor802 is authorized to decrypt content on behalf of the original secure microprocessor. Atblock812, assuming that the replacementsecure microprocessor802 is authorized to decrypt the media content, the escrowkey package316 is decrypted using the public key K_CH-PUBLICof thekey clearinghouse108 to produce the escrow key K_ESCRO. Atblock814, the escrow key is re-encrypted with the public key of the replacementsecure microprocessor804, here designated as K_SM2-PUBLICto produce E(K_SM2-PUBLIC(K_ESCROW)).
• Atblock816, an escrowkey recovery package818 is generated, which includes the newly encrypted escrow key E(K_SM2-PUBLIC(K_ESCROW)) as well as the identity of the original secure microprocessor430 (i.e. “SM1 Ident” inFIG. 8).
• The escrowkey recovery package818 is then transmitted back toDVR208 where replacementsecure microprocessor802 uses its private key K_SM2-PRIVATEto decrypt the escrow key recovery package atblock820 to obtain the escrow key K_ESCROalong with the identification (“SM1 IDENT”) of the originalsecure microprocessor430.
• Accordingly, now that the replacementsecure microprocessor802 has the identification and original escrow key of the originalsecure microprocessor430, the replacementsecure microprocessor804 can now decrypt anyescrow security packages608 created using the originalsecure microprocessor430. That is, becauseescrow security packages608 contain the content keys as encrypted by K_ESCRO, the replacementsecure microprocessor802 uses the recovered K_ESCROkey to decrypt the security packages608.
• FIG. 9 depicts a data flow diagram representing anembodiment900 for replacing escrowkey security packages608 created by the originalsecure microprocessor430 with corresponding escrow key security packages created by the replacementsecure microprocessor802. For clarity, the escrowkey security packages608 that are encrypted using the original escrow key ofsecure microprocessor430 are depicted inFIG. 9 as escrow key security packages “ESCROW SECURITY PACKAGE_SM1”, while the replacement escrowkey security packages908 are depicted as “ESCROW SECURITY PACKAGE_SM2”
• Specifically, atblock902, the replacementsecure microprocessor802 retrieves the escrow key of the original secure microprocessor along with its associated identity and decryptsescrow security package608 created by the originalsecure microprocessor430 to obtain a content key K_cassociated with a desired instance of media content. Atblock904, the content key K_cis encrypted (i.e. re-encrypted) with an escrow key generated by the replacementsecure microprocessor802, here designated as K_ESCRO-SM2to produce E(K_ESCROW-SM2(K_c)).
• At block906 a new, replacement escrow security packageESCROW SECURITY PACKAGE_SM2908 is created and stored tointernal storage418. At this time, the escrow security package608 (i.e. ESCROW SECURITY PACKAGE_SM1) can be deleted. Accordingly, all of the content keys for allescrow security packages608 that were created by the originalsecure microprocessor430 can be recovered by replacementsecure microprocessor802, and replacementsecure microprocessor802 re-encrypts new security packages with its own escrow key for each of the escrow security packages that were created by the originalsecure microprocessor802.
• Accordingly, unlike the disclosed escrow key embodiments, according to conventional key recovery techniques, a cable head end recovers a content key for each instance of media content recorded to the remote DVR. In order to access the media content with a replacement secure microprocessor, the replacement secure microprocessor requests the content key for each instance of media content stored tointernal storage418 from the cable head-end. The content key is secured for transmission between the replacement secure microprocessor and the cable head end using asymmetric encryption and decryption. Such an approach requires tremendous bandwidth and, because the encryption is asymmetric, the processing power can be overwhelming. However, using the escrow key approach described herein, the head end (or other key clearinghouse) can delegate the authority to the replacement secure microprocessor to provide access to the content keys associated with encrypted media content on storage devices associated with the replacement secure microprocessor.
• FIG. 10 depicts a data-flow diagram representing an embodiment1000 for using an escrow key to facilitate the ability for multiple DVRs to share media content. For example, according to one embodiment, aclient DVR1002 can obtain an escrow key that was used to encrypt content keys used to encrypt instances of media content previously recorded and stored to a device associated withserver DVR1004. Thus, the escrow key can be used by theclient DVR1002 to decrypt one or more content keys used to secure media content to be accessed by theclient DVR1002. Theserver DVR1004 andclient DVR1002 can communicate over acommunication medium212 as described with respect toDVR208 andDVR208a(FIG. 2). For example, in some embodiments,DVR1004 andclient DVR1002 may share media content and/or necessary information for obtaining keys to decrypt the media content over the communication medium.
• Specifically, atblock1006,client DVR1002 can request media content fromserver DVR1004. Atblock1008, thesecure microprocessor1010 ofserver DVR1004 receives the request for media content and verifies whether theclient DVR1002 has appropriate permissions to access the requested media content previously encrypted bysecure media microprocessor1010. For example, the clientsecure microprocessor1012 can provide proof of its identity to the server secure microprocessor, and the serversecure microprocessor1004 can check a list of trusted devices to confirm that the client secure microprocessor is on the list. One skilled in the art will realize that a number of other approaches for verifying the permission of the client DVR to access the media content associated withserver DVR1004 could be used.
• Atblock1012, assuming that theclient DVR1002 has permission to access the requested media content, the serversecure microprocessor1010 encrypts the escrow key K_{ESCROW-SERVER}provisioned to securemicroprocessor1010 with the public key K_{CLIENT-PUBLIC}of the clientsecure microprocessor1014 to produce encrypted escrow key E(K_{CLIENT-PUBLIC}(K_{ESCROW-SERVER})).
• The encrypted escrow key E(K_{CLIENT-PUBLIC}(K_{ESCROW-SERVER})) is then transmitted toclient DVR1002 which, atblock1016, can decrypt the server's escrow key with the private key of the clientsecure microprocessor1014 to obtain the escrow key of the server DVR K_{ESCROW-SERVER}.
• Server DVR1004 can then send theescrow key package1018 and the associatedencrypted media data1020 to theclient DVR1002. As described above, among other information,escrow key package1018 contains an encrypted content key K_cthat was previously used to encryptmedia data1020. Theencrypted media data1020 represents, in digital form, the media content requested atblock1006.
• Atblock1022, theclient DVR1002 can decrypt theescrow key package1018 associated with the requested media content with the escrow key of the serversecure microprocessor1010 to recover the content key K_c. Atblock1022, the media data associated with the requested media content can be decrypted with the content key K_cto obtainclear media data1026. The clear media data may be used, for example, to display media content withintelevision210.
• Accordingly, systems and methods for the secure escrow and recovery of media device content keys has been described that makes use of a two-level symmetric key encryption scheme for DVR recording and playback and which allows a key clearinghouse to delegate individual content key recovery tasks to a replacement secure microprocessor in a user's DVR set top box. Embodiments of the escrow key scheme can also be used for sharing media content between two digital media devices.
• According to one embodiment, an initialization process is used to generate a strong symmetric key, called the escrow key, which is associated with a first secure microprocessor. The generated escrow key is encrypted with the public key of the key clearinghouse and an escrow key package is created and stored outside the secure microprocessor, such as on a local hard drive and/or archived at the key clearinghouse.
• Additionally, an embodiment of a process for recording and playback of content secured with the escrow key has been described. Upon starting a recording, the first secure microprocessor creates an escrow security package for the media content. The security package can include, among other information, the identity of the secure microprocessor and the encrypted content key. To playback the media content, the security package is delivered to the secure microprocessor, which decrypts the content key with its escrow key and delivers the content key to the device responsible for decrypting the media content from DVR storage.
• Further, an embodiment of a content recovery scheme has been described which can be used to play back media content previously encrypted by a first secure microprocessor when the first secure microprocessor is no longer available. An escrow key recovery request is sent to the key clearinghouse and the key clearinghouse confirms whether the replacement secure microprocessor is authorized to decrypt content on behalf of the original secure microprocessor. If the content transfer is authorized, the key clearinghouse decrypts the escrow key package with its private key to recover the escrow key. The head end then re-encrypts the escrow key with the new secure microprocessor public key and sends an escrow key recovery package to the replacement secure microprocessor. The replacement secure microprocessor decrypts the escrow key with its private key, and securely stores the escrow key. Because the new secure microprocessor may be decrypting security packages created by multiple older secure microprocessors, the replacement secure microprocessor stores the identify of the secure microprocessor with its associated escrow key. The replacement secure microprocessor re-encrypts the content keys in all security packages stored to the DVR storage device with its own escrow key. The updated security packages are then stored on the DVR hard drive for later use and the original security packages created by the original secure microprocessor can be deleted.
• Any process descriptions, steps, or blocks in the flow or data flow diagrams described herein and/or depicted in the attached figures should be understood as potentially representing modules, segments, or portions of code which include one or more executable instructions for implementing specific logical functions or steps in the process. Alternate implementations are included within the scope of the preferred embodiments of the systems and methods described herein in which steps or functions may be deleted, executed out of order from that shown or discussed, including substantially concurrently or in reverse order, depending on the functionality involved, as would be understood by those reasonably skilled in the art.
• Conditional language, such as, among others, “can,” “could,” “might,” or “may,” unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments could include, while other embodiments do not include, certain features, elements and/or steps. Thus, such conditional language is not generally intended to imply that features, elements and/or steps are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without user input or prompting, whether these features, elements and/or steps are included or are to be performed in any particular embodiment.
• It should be emphasized that many variations and modifications may be made to the above-described embodiments, the elements of which are to be understood as being among other acceptable examples. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims.

Claims (22)

1. A method for securing media content comprising:

generating, with a first processor of a media device, an escrow key for encrypting a plurality of content keys, the content keys for encrypting instances of media content;

encrypting, with the first processor of the media device, the escrow key with a public key of a key clearinghouse; and

storing the escrow key, encrypted with the public key of the key clearinghouse, in a storage location outside of the first processor of the media device.

2. The method ofclaim 1, further comprising:

encrypting an instance of media content to be stored on a first storage device of the media device with a content key;

encrypting the content key with the escrow key; and

storing the content key, encrypted with the escrow key, to the first storage device.

3. The method ofclaim 2, wherein the content key encrypted with the escrow key is stored to the first storage device in an escrow security package with an identity of the first processor.

4. The method ofclaim 2, further comprising:

retrieving the content key, encrypted with the escrow key, from the storage device;

decrypting the content key, encrypted with the escrow key, with the escrow key; and

decrypting the media content with the content key.

5. The method ofclaim 2, further comprising:

requesting a release of the escrow key associated with the first processor from the key clearinghouse, the request including the identity of a second processor.

6. The method ofclaim 5, wherein the step of requesting a release of the escrow key associated with the first processor from the key clearinghouse causes the key clearinghouse to:

determine whether the second processor is authorized to access the escrow key; and

if the second processor is authorized to access the escrow key, decrypt the escrow key, encrypted with the public key of the key clearinghouse, with a private key of the key clearinghouse.

7. The method ofclaim 6, wherein the key clearinghouse further:

re-encrypts the escrow key with a public key of the second processor; and

delivers the escrow key, encrypted with the public key of the second processor, to the second processor.

8. The method ofclaim 7, further comprising:

decrypting the escrow key, encrypted with the public key of the second processor, with the private key of the second processor;

decrypting the content key, encrypted with the escrow key, with the escrow key; and

decrypting the instance of media content with the content key.

9. The method ofclaim 1, wherein the first processor is a secure microprocessor.

10. A digital media device comprising:

logic configured to generate an escrow key, associated with a first processor of the digital media device, for encrypting a plurality of content keys for encrypting instances of media content;

logic configured to encrypt the escrow key with a public key of a key clearinghouse; and

logic for storing the escrow key, encrypted with the public key of the key clearinghouse, in a storage location outside of the first processor of the media device.

11. The digital media device ofclaim 10, further comprising:

logic for encrypting an instance of media content to be stored on a first storage device of the media device with a content key;

logic for encrypting the content key with the escrow key; and

logic for storing the content key, encrypted with the escrow key, to the first storage device.

12. The digital media device ofclaim 11, wherein the logic for storing the content key, encrypted with the escrow key, to the first storage device includes logic for storing the content key to the first storage device in an escrow security package with an identity of the first processor.

13. The digital media device ofclaim 11, further comprising:

logic for retrieving the content key, encrypted with the escrow key, from the storage device;

logic for decrypting the content key, encrypted with the escrow key, with the escrow key; and

logic for decrypting the media content with the content key.

14. The digital media device ofclaim 11, further comprising:

logic for requesting a release of the escrow key associated with the first processor from the key clearinghouse, the request including the identity of a second processor.

15. The digital media device ofclaim 14, wherein the logic for requesting a release of the escrow key associated with the first processor from the key clearinghouse is configured to cause the key clearinghouse to:

determine whether the second processor is authorized to access the escrow key; and

if the second processor is authorized to access the escrow key, decrypt the escrow key, encrypted with the public key of the key clearinghouse, with a private key of the key clearinghouse;

re-encrypt the escrow key with a public key of the second processor; and

deliver the escrow key, encrypted with the public key of the second processor, to the second processor.

16. The digital media device ofclaim 15, further comprising:

logic for decrypting the escrow key, encrypted with the public key of the second processor, with the private key of the second processor;

logic for decrypting the content key, encrypted with the escrow key, with the escrow key; and

logic for decrypting the instance of media content with the content key.

17. An access control system for managing encryption keys associated with digital media device comprising:

a first digital media device having a first processor, the first processor configured to:

generate an escrow key for encrypting a plurality of content keys for encrypting instances of media content;

encrypt the escrow key with a public key of a key clearinghouse; and

store the escrow key, encrypted with the public key of the key clearinghouse, in a storage location outside of the first processor of the media device; and

a key clearinghouse for providing conditional access to the escrow key by a second processor.

18. The access control system ofclaim 17, wherein the digital media device is further configured to:

encrypt an instance of media content to be stored on a first storage device of the media device with a content key;

encrypt the content key with the escrow key; and

store the content key, encrypted with the escrow key, to the first storage device.

19. The access control system ofclaim 18, wherein the digital media device is further configured to:

retrieve the content key, encrypted with the escrow key, from the storage device;

decrypt the content key, encrypted with the escrow key, with the escrow key; and

decrypt the media content with the content key.

20. The access control system ofclaim 18, further comprising:

a second media device having a second processor, the second media device configured to request a release of the escrow key associated with the first processor from the key clearinghouse, the request including the identity of a second processor.

21. The access control system ofclaim 20, wherein the key clearinghouse is configured, in response to receiving the request to release the escrow key associated with the first processor from the key clearinghouse, to:

determine whether the second processor is authorized to access the escrow key; and

if the second processor is authorized to access the escrow key, decrypt the escrow key, encrypted with the public key of the key clearinghouse, with a private key of the key clearinghouse;

re-encrypt the escrow key with a public key of the second processor; and

deliver the escrow key, encrypted with the public key of the second processor, to the second processor.

22. The access control system ofclaim 21, wherein the second processor is further configured to decrypt the escrow key, encrypted with the public key of the second processor, with the private key of the second processor, and decrypt the content key, encrypted with the escrow key, with the escrow key; and

wherein the second media device is configured to decrypt the instance of media content with the content key.

Images